When devolatilization treatment is implemented on synthetic rubber, a treatment subject supplied to an extruder is typically constituted by rubber dissolved in a solvent obtained from a polymerization tank in a previous process. When the treatment is implemented using a conventional extruder, the rubber from which the solvent has been removed is pelletized by extremely reducing a throughput of the rubber per hour so as to suppress shear heating by the screw.
A configuration disclosed in Patent Document 1 may be cited as a vented twin-screw extruder used to devolatilize the solvent.
In FIG. 2, a reference symbol 1 denotes a cylinder assembly constituted by first to seventh segment cylinders 1a to 1g. The cylinder assembly 1 includes a raw material supply port 3, a first vent port 4a, and a second vent port 4b provided at intervals in sequence from an upstream side. A first devolatilization agent injection nozzle 7a and a second devolatilization agent injection nozzle 7b for injecting a devolatilization agent are provided on respective upstream sides of the first and second vent ports 4a, 4b. A first kneading portion 6a extending from the vicinity of an upstream side of the first devolatilization agent injection nozzle 7a to the vicinity of the upstream side of the first vent port 4a and a second kneading portion 6b extending similarly between the devolatilization agent nozzle 7b and the second vent port 4b are provided on two screws 2 disposed in the cylinder assembly 1.
Further, in a polymer recovery method according to Patent Document 2, not shown in the drawings, a polymer containing water is supplied to a twin-screw extruder in which a dewatering slit is provided in a bottom surface of a cylinder, and the polymer is moved through the extruder from a supply side to an discharge side while being gradually pressed and heated. The polymer is then extruded from a high pressure region to a low pressure region in an discharge side end portion of the extruder so that moisture remaining in the polymer is instantaneously vaporized, and as a result, the polymer is dried. According to this method, the extruder does not include a vent on the discharge side of the position in which the dewatering slit is installed, and therefore the extruded polymer can be foamed by the vaporized moisture and dried evenly.                Patent Document 1: Japanese Patent Application Publication No. H8-207118        Patent Document 2: Japanese Patent Application Publication No. 2000-310482        